Photothermal IR Spectroscopy in Life Science and Biological Applications

Photothermal IR is a breakthrough technique that has opened up new applications for infrared spectroscopy in life science and pharmaceuticals. This new analytical method can used in your lab with the mIRage optical IR spectroscopy and imaging system from Photothermal Spectroscopy Corp.

Blue Scientific is the official distributor for Photothermal Spectroscopy Corp in the UK, Ireland and Nordic region (Norway, Finland, Sweden, Iceland, Denmark). For more information or quotes, please get in touch.

mIRage IR microscope

 Contact us on +44 (0)1223 422 269 or


New IR Applications in Life Science

Traditionally, infrared spectroscopy has been limited to analysing molecular vibrational absorption for chemical specificity. However, a new technique based on photothermal microscopy has now opened up infrared spectroscopy to new applications.

One such application is bioanalysis, an area where it has previously been difficult to study how molecules perform in a living system, because of the challenges in gathering data about spatial and temporal dynamics.

Photothermal IR spectroscopy (O-PTIR) is an extremely sensitive, nanoscale chemical imaging technique, that measures the visible beam of the thermo-refractive effect of IR absorption. This opens up new biological applications for infrared, such as:

  • Mapping drug distribution in pharmaceutical formulations
  • Studying metabolic activities inside a living cell
Porcine Stem Cell

Porcine stem cell – Reflection mode single wavelength image (1540 cm-1) extracted from hyperspectral data set. 30 x 30 µm image with 500 nm point spacing, 1 spectrum/point (1s).

Overcoming the Limitations of IR

Traditional IR imaging has several critical limitations in life science:

  • Poor spatial resolution
  • Lack of depth resolution
  • Not suitable for living systems, because of water absorption

O-PTIR overcomes these limitations. An optical beam is used to measure the sample’s photothermal response due to IR absorption. The visible optical beam in the mIRage can be focussed 20 times smaller than the IR beam, for significantly enhanced spatial resolution compared to a conventional IR microscope. Spectra are acquired by sweeping the IR laser wavelengths, and chemical maps can be built by scanning the sample. The technique has many benefits:

  • Highly sensitive
  • Fast imaging
  • Molecular fingerprint information
  • Micromolar sensitivity
  • Sub-micron spatial resolution
  • Suitable for liquid and solid samples

High Spatial Resolution

The increased spatial resolution of O-PTIR brings new possibilities to IR spectroscopy:

  • Subcellular structures in living cells
  • Single bacteria imaging
  • Drug uptake in living cells
  • Metabolites in live cells
  • Lipid and protein imaging
  • Concentration distribution mapping
  • Live organisms and tissue slices

As an example, the technique has been used to map lipid droplets and membranes in cancer cells, which are highly relevant to metabolic processes. Lipid droplet distribution can be visualised clearly within individual cells, with each droplet clearly visible. Sectioning images were acquired by changing the depth. This enabled the lipid droplets to be mapped in 3D, within the single cell. Further details and example images are available in an article in Photonics Media.

More Examples

Photonics Media have published an article by researchers from Boston University about how mid-infrared is being used in new biological applications:

Article: Photothermal IR Spectroscopy Boosts Chemical Microscopy, Expands Applications

How O-PTIR Works

Mid-infrared photothermal microscopy MIP bridges the gap between FT-IR (Fourier transform spectroscopy) and AFM-IR (Atomic Force Microscopy combined with IR spectroscopy).

Mid IR Spectroscopy

A mid-IR pulsed, tunable laser heats the sample. When the IR laser reaches a wavelength that causes molecular vibration in the sample, absorption occurs. This creates photothermal effects, which are measured by a visible probe laser that’s focused to a 0.5 µm spot size. This is how O-PTIR overcomes the usual IR diffraction limit.

The part of the reflected visible laser signal that’s modulated at the IR pump laser repetition rate is directly proportional to the absorption coefficient of the sample at that particular wave-number. The IR pump laser can got through through the entire fingerprint range in a second or less, which provides an IR spectrum.

O-PTIR works in reflection mode, which gives you sub-micron resolution from a non-contact optical method.

Measurements are collected quickly and easily without sample contact. Spectra quality is comparable to FT-IR, but without the dispersive artifacts that are such common problem in ATR. Because it uses reflection mode, samples do not need to be thin. Sample preparation is therefore simpler and the whole process is faster.


Click to enlarge

PhotoThermal Mirage IR Microscope

mIRage IR Microscope

The mIRage from Photothermal Spectrocopy Corp is a new system that enables you to use O-PTIR in your lab:

  • Fast and easy to use
  • Transmission FT-IR quality spectra
  • Flexible system for a range of applications

More info…

Blue Scientific is the official distributor of the mIRage in the UK, Ireland and Nordic region. If you have any questions or if you’d like a quote, please get in touch:

 Contact us on +44 (0)1223 422 269 or

mIRage IR microscope